1. Field of the Invention
The present invention relates to a recirculating molten metal supply system and, more particularly, to a molten metal supply system in which molten metal is continuously circulated between a melting furnace and a holding furnace for providing a clean and uniform temperature molten metal supply to a casting machine, a molten metal degassing furnace, a molten metal filtration system, and the like.
2. Description of the Prior Art
A typical casting apparatus for casting metal component parts includes a supply tank configured to contain molten metal. The supply tank is typically in fluid communication with an injection device for injecting the molten metal into a casting machine located outside the supply tank. The supply tank may be a molten metal holding furnace that contains the molten metal. The supply tank, or holding furnace, is typically heated to maintain a substantially constant, preset molten metal temperature in the holding furnace. Numerous methods are known in the art for heating molten metal in a holding furnace. Several common examples include induction heating, radiant heating, and immersion heating.
The holding furnace is often supplied with molten metal from a larger furnace. Once a supply or xe2x80x9cbatchxe2x80x9d of molten metal is received in the holding furnace, the holding furnace through its internal or external heating devices attempts to maintain the molten metal substantially at a preset temperature. The holding furnace then supplies the molten metal to, for example, an injection device for injecting the molten metal into a casting machine.
As the supply of molten metal in the holding furnace decreases, it becomes progressively more difficult to maintain a set molten metal temperature in the holding furnace. U.S. Pat. No. 4,753,283 to Nakano discloses a typical example of the foregoing. This reference discloses a horizontal injection casting machine in which molten metal is maintained in a heat retaining furnace, or holding furnace, which periodically provides molten metal to the casting machine. Over time, the amount of molten metal in the heat retaining furnace steadily decreases making it progressively more difficult to maintain a set molten metal temperature in the heat retaining furnace. Further, the heat retaining furnace must be periodically supplied or refilled with a new xe2x80x9cbatchxe2x80x9d of molten metal from a smelting furnace.
As stated hereinabove, a disadvantage with xe2x80x9cbatchxe2x80x9d type holding furnace arrangements is that as the supply of molten metal in the holding furnace decreases, it becomes progressively more difficult to maintain the temperature of the molten metal. An additional disadvantage is that as the supply of molten metal in the holding furnace decreases, the impurity level in the remaining molten metal increases. As a result, the quality of the metal component parts decreases with each injection cycle of molten metal into the casting machine. Further, in order to supply the holding furnace with a new xe2x80x9cbatchxe2x80x9d of molten metal, the cover of the holding furnace must typically be removed, which is a time consuming process.
One known solution to the foregoing disadvantages is to arrange the holding furnace and a larger smelting or xe2x80x9csupplyxe2x80x9d furnace as a single, two-chamber furnace. Such two-chamber xe2x80x9cmeltxe2x80x9d furnaces may be used in combination with a casting machine. Such two-chamber melt furnaces typically include a heating chamber in which the molten metal is heated, and a removal chamber which stores the molten metal prior to delivering the molten metal to a casting machine. An intermediate chamber may be located between the heating chamber and the removal chamber, which is used to maintain a fixed level of molten metal in the removal chamber by continuously circulating molten metal from the heating chamber to the removal chamber.
A two-chamber melt furnace similar to that discussed hereinabove is disclosed by U.S. Pat. No. 5,411,240 to Rapp et al. The two-chamber melt furnace disclosed by the Rapp et al. patent includes a pump located in an intermediate storage chamber that continuously delivers heated molten metal from a heating chamber to a removal chamber. The pump is also used to recirculate molten metal from the removal chamber back to the heating chamber. The Rapp et al. patent utilizes an overflow pipe in the intermediate chamber to control the molten metal level in the removal chamber.
In view of the foregoing, an object of the present invention is to provide a recirculating molten metal supply system in which a uniform molten metal temperature may be maintained throughout the system. In addition, it is an object of the present invention to provide a recirculating molten metal supply system in which a clean supply of molten metal is continuously supplied to a casting machine for improving the quality of cast metal components formed in the casting machine. It is a further object of the present invention to provide a method of molten metal injection to a casting machine that improves the quality of cast metal components formed in the casting machine.
The above objects are accomplished with a molten metal supply system for supplying molten metal to a casting machine in accordance with the present invention. The molten metal supply system includes a holder furnace, a casting mold, at least one molten metal injector, and a melter furnace. The holder furnace defines a molten metal receiving chamber. The casting mold is located above the holder furnace and defines a mold cavity for casting metal components. The injector is supported from a bottom side of the casting mold and extends downward into the molten metal receiving chamber. The injector provides fluid communication between the molten metal receiving chamber and the mold cavity. The injector is configured to inject molten metal received into the molten metal receiving chamber into the mold cavity.
The melter furnace is located externally adjacent to the holder furnace and is in fluid communication with the holder furnace through a pair of conduits. The conduits include a first conduit for supplying molten metal to the molten metal receiving chamber, and a second conduit for recirculating molten metal from the molten metal receiving chamber to the melter furnace. The melter furnace further includes a heating chamber, a pump chamber, a degassing chamber, and a filter chamber.
The heating chamber is in fluid communication with the molten metal receiving chamber through the second conduit and receives molten metal recirculating back through the second conduit from the holder furnace. The pump chamber is located adjacent the heating chamber and houses a molten metal pump. The pump has an inlet in fluid communication with the heating chamber and has an outlet. The pump is configured to circulate molten metal through the molten metal supply system during its operation. The degassing chamber is located adjacent the pump chamber and houses a degassing mechanism. The outlet of the pump is in fluid communication with the degassing chamber and provides molten metal to the degassing chamber during operation of the molten metal supply system. The filter chamber is located adjacent and in fluid communication with the degassing chamber. The filter chamber is in fluid communication with the molten metal receiving chamber through the first conduit for supplying degassed and filtered molten metal to the molten metal receiving chamber during operation of the molten metal supply system.
The molten metal receiving chamber may define a plurality of vertically extending chambers connected in series. A plurality of molten metal injectors may be supported from the bottom side of the casting mold. The injectors may cooperate, respectively, with the plurality of vertically extending chambers.
The heating chamber may include a burner device for heating the molten metal contained therein during operation of the molten metal supply system. The degassing mechanism may be a rotary degassing mechanism. The filter chamber may include a molten metal filter configured to filter particles larger than about 50-80 microns.
The present invention is also a method of supplying molten metal to a casting machine. The method may include the steps of: providing a casting machine comprising a casting mold defining a mold cavity for casting metal components, a holder furnace located beneath the casting mold for supplying molten metal to the mold cavity, and a melter furnace externally positioned adjacent the holder furnace for supplying molten metal to the holder furnace; filling the melter furnace with molten metal; placing the holder furnace in fluid communication with the casting mold; placing the melter furnace in fluid communication with the holder furnace through a first conduit for supplying molten metal to the holder furnace, and through a second conduit for recirculating molten metal from the holder furnace to the melter furnace, with the melter furnace further comprising a heating chamber, a pump chamber, and a degassing chamber; heating molten metal in the heating chamber; pumping molten metal from the heating chamber to the degassing chamber and the filter chamber with a pump; degassing the molten metal into the degassing chamber; filtering the molten metal in the filter chamber; supplying degassed and filtered molten metal to the holder furnace through the first conduit; and continuously recirculating molten metal from the holder furnace to the heating chamber through the second conduit.
The method may include the step of supporting a plurality of molten metal injectors from a bottom side of the casting mold, with the injectors configured to provide fluid communication between the holder furnace and the casting mold. The holder furnace may define a molten metal receiving chamber having a plurality of vertically extending chambers connected in series. The method may further include the step of receiving the molten metal injectors into the vertically extending chambers, respectively, with the injectors placing the vertically extending chambers in fluid communication with the mold cavity.
The method of the present invention may further include the steps of: passing molten metal to the vertically extending chambers through the first conduit; pumping molten metal through the vertically extending chambers to maintain a substantially constant level of molten metal in the vertically extending chambers; receiving molten metal into each of the injectors; and injecting molten metal into the mold cavity with the injectors at different times and at different rates to completely fill the mold cavity.
The degassing mechanism may be a rotary degassing mechanism, and the method may further include the step of supplying a mixture of about 0.1 to 10% chlorine with a balance of one of argon and nitrogen gas to the molten metal in the degassing chamber with the rotary degassing mechanism to degas the molten metal passing through the degassing chamber.
A molten metal level sensor may be located in the filter chamber, and the method may further include the steps of: monitoring the level of molten metal in the filter chamber with the level sensor; and sending a cutoff signal to the pump when the level of molten metal in the filter chamber reaches a predetermined level.
Finally, the method may include the step of internally circulating molten metal in the melter furnace through a bypass conduit connecting the filter chamber and the heating chamber.
Further details and advantages of the present invention will become apparent from the following detailed description read in conjunction with the drawings.